The present invention relates to a method for the preparation of an organopolysiloxane or, more particularly, to a method for the preparation of an organopolysiloxane by the ring-opening or equilibration polymerization of organopolysiloxane oligomers in the presence of an acid catalyst, in which the amount of residual silanolic terminals is greatly decreased so as to impart the organopolysiloxane with improved heat stability and curing characteristics.
It is well known in the art of silicones that a high-polymeric organopolysiloxane can be prepared by the polymerization of organopolysiloxane oligomers in the presence of a strong acid or strong basic compound as the catalyst. When a strong acid is used as the catalyst, it is usual that completion of the polymerization is followed by the neutralization of the acid in the mixture after washing with water by the addition of an alkaline compound such as sodium carbonate, sodium hydrogencarbonate or ammonium carbonate.
A problem in such a process of neutralization by the addition of the alkaline compound is that the neutralization is complete taking a considerably long time because the above mentioned neutralizing agents are each solid. Moreover, the organopolysiloxane prepared in the above described method contains a considerably large amount of silanolic hydroxy groups at many of the molecular chain ends badly affecting the heat stability and curing characteristics of the organopolysiloxane
When the polymerization is performed in the presence of an alkaline compound as the catalyst, the alkalinity after completion of the polymerization reaction is neutralized usually using an ammonium halide, alpha-halohydrin and the like while neutralization with such a neutralizing agent can hardly be complete in addition to the problem that the thus neutralized organopolysiloxane necessarily contains more or less of halogen as an impurity to cause various adverse influences. Alternatively, a method has been proposed in Japanese Patent Kokai 60-49033 that the residual alkaline catalyst is neutralized by the addition of a triorgano halosilane and a hexaorgano disilazane. This method, however, is disadvantageous in respect of the low yield of the desired organopolysiloxane.